Makarova broke serve six times and was 15 of 20 on second serve return points in her 52-minute, 6-1, 6-1 triumph over Rybarikova, who came into this week 10-0 at this tournament but has now dropped five straight matches.

"It wasn't as easy as the score indicated," Makarova said. "There were a lot of deuce games, and the points were all long. I'm really happy that I was aggressive, solid and focused."

Makarova had lost her first two encounters with Rybarikova, including a semifinal defeat here last year in which she mustered just two games. She was playing for the first time since her Wimbledon quarterfinal loss to Lucie Safarova.

No.4 seed Sloane Stephens also exited Washington DC at the hands of fellow WTA Rising Star Christina McHale, who converted on six of seven break points in her 6-4, 4-6, 6-0 victory.

"Sloane and I hadn't played since the juniors," McHale said. "It was a really tough match, and I'm just happy that I pulled through and advanced to the next round.

"It was a big win for me. I love playing in the US Open Series. This is a good start for me, as I hadn't played a match in a month. It just felt good to be back on the court."

Another WTA Rising Star, Lauren Davis, rallied from a 6-1, 3-1 deficit en route to a 1-6, 6-4, 6-2 win over Peng Shuai in the American's first match since losing to Peng in the third round of Wimbledon.